The main purpose of a grid is to display information from a table. Grids show a number of columns which represent fields, however, not all fields are shown.
The Advanced Search allows a user to search through other fields which may not be shown on the grid. However, these fields need to be added to the advanced search.
In order to add more fields to the advanced search, you need to customize the grid.
Below we will outline how to add other fields by using the Estimates List screen as an example. The steps will be the same for any screen that has a grid on it.
Customizing a Grid
In this example, we will customize the Estimates List screen and add the Assigned To field to advanced search.
While viewing the Estimates List screen, click the down arrow icon
by the Estimates header and then click Customize Screen. 
You will be notified that the screen is in read-only mode. Click the Edit button.
Since the screen is one of our stock screens, you will be asked to create a copy of it. Click Create copy.
Find the Estimates grid and select it. Its properties will appear on the right properties panel.
Scroll down in the properties. Find and expand Filters & Views, and then select Search Fields.
A dialogue box pops up. Click ⊕ Add search field.
In the dropdown, select AssignedTo field. Feel free to add any other field you may wish to add to the advanced search.
You are done! Click Save & Close.
Then Save to save the screen, and finally Close.
And now your grid's Advanced Search will search through the AssignedTo field.